For me it's when I play against Imp and I can hear him blush through the microphone.
Obvious statements aside, it's something that helps distract me when I'm not feeling great, when the parts of my brain that get stimulated by emotions or beauty are quite dead (mostly due to physical stress). Despite its reputation, it can be a somewhat low effort game too. I don't play chess when I'm doing great, which could be why I suck at it lol.
When I was a kid though I used to play on a real chess board sometimes and it had a real nice sensory charm to it, the wooden pieces beautifully carved and nice to the touch, the face to face with your friend, the moves viewed in 3 dimensions... it was much nicer than online. It's a beautiful game especially if you love the feeling of saving things in your mind.
for me chess isn't fun in the same way a video game is.